Science — CBSE Class 10 board question

(i) Double Circulation:
When blood passes through the heart twice during one complete cycle through the body, it is called double circulation. Blood goes once to the lungs (pulmonary circulation) and once to the rest of the body (systemic circulation).

(ii) Separation of right and left sides:
The separation prevents oxygenated and de-oxygenated blood from mixing, allowing a highly efficient supply of oxygen to the body.

Birds and mammals are warm-blooded — they constantly use energy to maintain body temperature. This requires a continuous, efficient oxygen supply. The complete separation of the two sides of the heart ensures oxygen-rich blood is always pumped to body tissues without dilution, meeting their high energy demands.

Source: Chapter 5, Section 5.4.1

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• Part (i) is worth ~1 mark: one crisp definition focusing on "twice through the heart" and naming both circuits.
• Part (ii) is worth ~2 marks: state the purpose (no mixing → efficient O₂ supply) and then specifically link to birds/mammals being warm-blooded with high energy needs. Examiners expect both the general benefit and the specific application to warm-blooded animals.